Liquid nitrogen (finally) makes an Arduino project cool. Overclocking Arduino with liquid nitrogen cooling. 20⇒65.3Mhz @-196°C/-320°F article has this video that shows how it is done.
It turns out that you can run an Arduino UNO at 65.3MHz when it is cooled with liquid nitrogen. Arduino UNO / ATmega328P at 8V is stable at 65.3Mhz when cooled with liquid nitrogen, while at room temperature – only at 32.5-37Mhz while the manufacturer rated the part only up to 20 MHz. Is this useful? Probably not. Is this a cool hack? Yes.